From e111def44a7df4624a4aa3f85fe98054bffb6b4f Mon Sep 17 00:00:00 2001
From: Trent Lloyd <trent@lloyd.id.au>
Date: Sat, 22 Dec 2018 09:06:07 +0800
Subject: [PATCH] Drop legacy unicast queries from address not on local link

When handling legacy unicast queries, ensure that the source IP is
inside a subnet on the local link, otherwise drop the packet.

Fixes #145
Fixes #203
CVE-2017-6519
CVE-2018-100084
---
 avahi-core/server.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/avahi-core/server.c b/avahi-core/server.c
index a2cb19a8..a2580e38 100644
--- a/avahi-core/server.c
+++ b/avahi-core/server.c
@@ -930,6 +930,7 @@ static void dispatch_packet(AvahiServer *s, AvahiDnsPacket *p, const AvahiAddres
 
     if (avahi_dns_packet_is_query(p)) {
         int legacy_unicast = 0;
+        char t[AVAHI_ADDRESS_STR_MAX];
 
         /* For queries EDNS0 might allow ARCOUNT != 0. We ignore the
          * AR section completely here, so far. Until the day we add
@@ -947,6 +948,13 @@ static void dispatch_packet(AvahiServer *s, AvahiDnsPacket *p, const AvahiAddres
             legacy_unicast = 1;
         }
 
+        if (!is_mdns_mcast_address(dst_address) &&
+            !avahi_interface_address_on_link(i, src_address)) {
+
+            avahi_log_debug("Received non-local unicast query from host %s on interface '%s.%i'.", avahi_address_snprint(t, sizeof(t), src_address), i->hardware->name, i->protocol);
+            return;
+        }
+
         if (legacy_unicast)
             reflect_legacy_unicast_query_packet(s, p, i, src_address, port);
 
